Environmental Effects of Acid Rain
The most obvious environmental effect of acid rain has been the loss of fish in acid sensitive lakes and streams. Many species of fish are not able to survive in acidic water. Acid rain affects lakes and streams in two ways: chronic and episodic. Chronic, or long-term acidification results form years of acidic rainfall. It reduces the alkalinity (buffering capacity) and increases the acidity of the water. Chronic acidification may reduce the levels of nutrients such as calcium, which, over time, may weaken the fish and other plants and animals in an aquatic ecosystem. Episodic acidification is a sudden jump in the acidity of the water. This can result from a heavy rainstorm. It also happens in the spring, because the sulfates and nitrates will concentrate in the lowest layers of a snowpack. In the spring, when that snow melts, it will be more acidic than normal. Episodic acidification can cause sudden shifts in water chemistry. This may lead to high concentrations of substances such as aluminum, which may be toxic to fish.
Most of the effects on forests are subtle. Acid deposition may influence forest vegetation and soils. Acid rain weakens the trees’ natural defenses, making them more vulnerable to diseases. Acid rain has been cited as a contributing factor to the decline of the spruce-fir forests throughout the Eastern United States. Acid rain may remove soil nutrients such as calcium and magnesium from soils in high elevation forests and cause damage to needles of Red Spruce. Acid rain may also help weaken natural defenses of some trees, making them more vulnerable to some diseases and pests.
Acid rain deposits nitrates that can lead to increases in nitrogen in forests. Nitrogen is an important plant nutrient, but some forest systems may not be able to use all they receive, leading to nitrogen saturation. In the Eastern United States, there is evidence of nitrogen saturation in some forests. Nitrates can remove additional calcium and magnesium from the soils. Continued nitrogen deposition may alter other aspects of the nutrient balance in sensitive forest ecosystems and alter the chemistry of nearby lakes and streams.
Excess nitrogen may cause eutrophication (over nourishment) in areas where rivers enter the ocean. This may lead to unwanted growth of algae and other nuisance plants. As much as 40% of the total nitrogen entering coastal bays on the Atlantic and Gulf Coasts may come from atmospheric deposition. Table I shows estimates of the percentage of nitrogen deposition which comes from the atmosphere.

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